Thermoelectric devices and methods of making same



Jan. 29, 1963 v. HABA 3,076,05

THERMOELECTRIC DEVICES AND METHODS oF MAKING vSAME Filed March 5, 1959PIN P||Al .ZI-7%. .5. I l/Z dtihl Patented dan. 29, lgd'l ice d, i959,Ser. No. iM-)7,427 lil C.. s. (El. 'i3d-4) The present invention relatesto thermoelectrics, and more particularly to improved thermoelectricdevices and to methods for making such devices.

Thermoelectric devices may be used in providing thermoelectric heatpumps suitable for heating and cooling. Electric power generation mayalso be accomplished with thermoelectric devices. Therrnoelectricdevices are, fundamentally, structures comprising bodies of dissimilarthermoelectric materials which are electrically interconnected. Thesedissimilar thermoelectric materials are categorized as either N or ltypes, depending upon the direction of the current iiov/iug across ajunction between the bodies of such materials producing heating orcooling at the junction.

Thermoelectric materials heretofore known and proposed for the abovepurposes have several disadvantages. For example, they are usuallybrittle and subject to iracture under rough handling. rIhre heat pumpingand/or power generating capacity of a single tnermocouple formed by tivobodies of dissimilar thermoeiectric rnaterial is small as compared tothe heat pumping and/or power generating capacity of a large number ofsuch bodies. Heat due to loulean losses decreases the heat pumpingefficiency of tliermoelectric devices.

Several devices have been constructed incorporating improvements foreliminating one or more or" the foregoing disadvantages. While thesedevices have been more or less suitable for their intended purpose, theyare not sufficiently flexible for universal application inthermoelectric apparatus useful for heating, cooling or powergeneration.

lt is therefore an object of the present invention to provide improvedthermoelectric devices wherein the foregoing disadvantages areeliminated, as Well as to provide methods oi' making such devices.

lt is another object of the present invention to provide improvedthermoelectric devices which are protected against breakage and aretherefore easily handled, and also to provide methods of making suchdevices.

It is still another object or the present invention to provide improvedthermoelectric devices ivi 'ch contain a larger number of elements in agiven area t' an was ador-ded by former thermoelectric devices and whichtherefore possess greater heat pumping and electrical power generatingcapacity than devices heretofore available, as Weil as to providemethods or making such improved thermoelectric devices.

it is a further object or" the present invention to provide a method ofmaking arrays or" thermocouple elements of any desired size to therebypresent cold and hot suraces of any desired area.

lt is a still further object of the present invention to provideimproved therme-electric devices and a method of miniaturizing suchdevices.

lt is a still further object of the present invention to provide animproved thermoelectric panel device of lower cost than previous devicesof this type, and also a simplied method or" manufacturing such animproved thermoelectric panel device.

Brieiiy described, a thermoeiectric device provided in accordance withthe present invention may include a plurality of bodies ofthermoelectric materials which are disposed in a matrix enveloping thesebodies. The matrix includes a plurality of adjacent layers of insulatingmaterial, auch as epoxy casting resins having different heat transferproperties, which results in greater heat pumping emciency andestablishes a steeper temperature gradient across the device.

A method of making the improved thermoelectric device in accordance withthe invention may comprise the steps of arranging bodies of dissimilarthermoelectric material in an ordered array, and then casting one ormore layers of insulating material so as to surround and bind saidbodies in said ordered array. In this manner, a thermoelectric panelmatrix may be provide which is a unitary structure which provides forease of handling, protection against breakage and large heat pumpingcapacity.

The invention itself, both as to its organization and method ofoperation, as well as the foregoing and other objects and advantagesthereof, will become more readily apparent from a reading of thefollowing description in connection with the accompanying drawing inwhich:

FlGS. l to 4 show a thermoelectric device provided by the presentinvention at different stages of manufacture;

FlG. 5 is a perspective View showing a completed thermoelectric deviceprovided in accordance with the present invention; and

FlG. 6 is a sectional view of another embodiment of a thermoelectricdevice provided by the present invention.

Referring, now, more particularly to FIGS. l to 5 of the drawing, aplurality of bodies .lo and l2 of thermoelectric material are shown.Some of the bodies, such as the bodies lil, are labeled with the letterR While the remaining bodies l2 are labeled with the letter l rl`hematerial of the P-type bodies lil and the material of the N-type bodiesil?. are dissimilar thermoelectrically. The identiiication or thematerials as being P or N types is in accordance with the conventionsused in semiconductor technology. The preparation or P-type and N-typetliermoelectric materials is not a part of the present invention.Examples of such materials are described in detail in patents issued inthe name of Nils E. Lindenblad, Nos. 2,846,493 and 2,846,494. Anothermaterial from which the bodies lil and l2 may be made is bismuthtelluride which is properly alloyed with various minor impurities so asto provide N-type material for one group of bodies l?. and lD-typematerial for the other group of bodies lo. The preparation of suchmaterials is described in an application led in the name of C. l.Busanovich,

erial No. 609,255 `on September ll, i956, now US. Patent 2,932,529, andassigned to Radio Corporation of America.

These thermoelectric materials are very brittle and are prone to crackor shatter if dropped or otherwise roughly handled. it is a feature orthe present invention to provide a matrix containing a large number ofbodies of thermoelectric material enveloped by another material whichwill protect the thermoelectric bodies against breakage.

While an larray of sixteen bodies lil and l2 of thermoelectric materialis shown in the drawing for purposes of illustration, a much largernumber of bodies of thermoelectric material may be used. As Will bedescribed hereinafter, many thermoelectric devices may be made bysub-dividing a large group assembled elements into smaller groups.

Referring, now especially, to FGS. l to 4, the method of making athermoelectric device in accordance with the present invention will beset forth. A plurality of bodies of the thermoelectric material lltl andl2 are placed in an ordered array in a mold form ld. This mold form maybe made of steel or cast iron, for example. The dissimilar P-type andN-type bodies of tlierrnoelectric material are disposed alternately inrather closely adjain .which they were placed inthe moldld.

u cent relation. 'The bottom or base of the mold is ilat. The end facesof the bodies of thermoelectric material are also ilat. Each body ofthermoelectric material is a rectangular slug of the sameheight andcross sectional dimensions. However, the bodies may also be round,triangular, hexagonal, or of any other convenient shape. The end facesof the bodies l and i2 which extend from the mold 1d are in a commonplane, as are the o-pposite end faces which are disposed on the bottomof the mold. Any number of such bodies may be used. The heatv pumpingand power generating capacity of a thermorelectric device depends uponthe number of thermo couple elements in the device. Accordingly, a largearray of thermocouples may be provided in a thermoel-ectric .deviceconstructed in accordance with the invention. While the bodies of thethermoelectric material are shown as being of greater height than width,a thermoelectric device may be provided in accordance with the presentinvention wherein the bodies are of lesser height. The height of thebodies of thermoelectric material maybe of the order of theirwidth, ifdesired.

The ,entire thermoelectric device provided by the presentinvention mayalso be very small in size. The bodies 10 and 12 of thermoelectriematerial shownin FIG. l may be miniaturized to a large extent. Forexample, a thermoelectric device may be provided by the practice of thisinvention which contains bodies of thermoelectric material one-.tenththe size of thebodies of thermoelectric material shown in the drawing.Such microminiaturization is made possible by the matrix arrangement ofthe thermoelectric elements, as will be described hereinafter.

After the bodies of thermoelectric material are disposed inordered arrayin the mold ld, a material which is easily dissolved or which has a lowmelting point, such as wax, is poured into the mold. Enough of thismaterial, which will be referred to as wax hereinafter to simplify thediscussio-n, is poured into the mold to reach a level approximatelyone-third the height ofthe bodies of thermoelectric material. The waxforms a smooth surface at a level intermediate the ends of the bodies ofthermoelectric material upon hardening. rl`his intermediate level in themold forms a base surface. After the wax has solidified, an insulatingmaterial is cast into the mold. Enough of this material is used to fillthe mold to a point about twothirds the height of the bodies ofthermoelectric material. The material which is cast into the mold isdesirably a plastic. A plastic of the epoxy type may be suitable. Theseepoxy plastics are epoxy resins which are in liquid form before pouringinto the mold. The resins are selfsetting at room temperature or atemperature slightly higher than room temperature. Thus, the use ofepoxy resins simplifies the construction ofthe thermoelectricdeviceprovided by the invention. It is desirable that the material whichis cast into the mold be heat resistant. VThis ,material should alsohave better heatY transfer characteristics than other materials whichwill surround it. An epoxy resin with a filler of expanded mica issuitable. Another epoxy resin which will be found suitable for use inthe casting process shown in FIG. l is identified by the trade nameStycast 3050.

The material which is cast into the mold over the wax is therefore inthe nature of a cement in this preferred embodiment of the presentinvention. The resin is permitted to solidify to provide a layer 20intermediate the ends of t-he bodies of thermoelectric material. Theepoxy resin in this layer 2@ adheres to the bodies l0 and l2 and bindsthem in the ordered array in which they were placed in the mold i4.

Thev epoxy resin forming the layer 20 desirably has a coecient ofexpansion substantially the same as the coefcient4 of expansion of thebodies l0 and l2. rl`his characteristic of the layer 2i? insures thatthe bodies of thermoelectric material will be maintained in the properposition It has been found that, during operation of the thermoelectricdevice, the bodies of thermoelectric material may have various operatingtemperatures. Even adjacent ones of the bodies it@ and l2 may be atdifferent temperatures. Since the coetiicient of expansion of the layer20 is substantially the same as the coei'iicient of expansion of thebodies it? and l2, there will be no stress developed in the layer 20 andno consequent bending or warping of the layer. The bodies i0 and i2.will, therefore, be maintained in their ordered array. Another advantageof the use of a bonding layer 2@ having substantially the same coeicientof expansion as the bodies ltxand i2 is that connectors, which will bedescribed hereinafter, which are attached to the opposite ends of thebodies `will not be loosened because of unwanted relative movements ofthe bodies.

The assembled'bodies l0 and l2 may be removed from the mold after thelayer 20 solidiiies and sets. With the material identified above asStycast 3050, such solidication and setting will be accomplished afterabout twenty minutes to fo-ur hours, depending upon thickness of thelayer and ambient'temperature. The wax may be removed from the assembledbodies wand 12and layer 2t) by heating after removal of the assembledbodies from the mold. If a soluble material were used in place of wax, asolvent will be used at this point to remove the soluble material.Electrical connectors 22 inthe form of copper plates are soldered to theends of the bodies l0 and 12. The connectors are soldered to adjacent Pand N type bodies to provide a continuous, series circuit through thebodies of thermoelectric material. .The end ones of these connectors 22may be extended to provide lugs 24 and 26, as shown in FIG. 5, forconnection to a source of operating current for the thermoelectricdevice. Alternatively,

" if the device is used as a power generator, electrical cur rent whichis generated will be available at the lugs 24 and 26. The plateconnectors 22 provide heat dissipating terminals or hot junctions on oneside of the device and heat absorbing terminals or kcold junctions onthe other side of the. device depending upon the direction of currentflow.

The layer 20 intermediate the ends of the bodies 10 and 12 is heatresistant and therefore simplifies soldering. Also, the position of thislayer Ztl, approximately onethird the distance from the ends of thebodies, simplifies the soldering operation since the entire surface ofthe ends of. the bodies may be tindipped and covered with solder by asimple dipping process. This soldering process provides a very lowresistance bond. The process is described in detail in my copendingpatent application tiled on September 14, 1956, Serial No, 609,940, nowPatent No. 3,017,693. Theprocess is particularlyrsuitable for :solderingthe connectors to bismuth telluridel materials. In accordance with theprocess, the surface of the bismuth telluride body is coated or dippedin a bismuth antimony-tin solder and the conductor` is coated or dippedin a tin-lead solder before joining the connectors and the bodies toeach other.

After the connectors 22 are in place, the assembled bodies 10 and l2 ofthermoelectric material, together with the intermediate layer 20 and theconnectors22, are placed in a mold 1S, which is desirably somewhatlarger than the mold 14. The surfaces of the lower connectors 22 aredisposed on the bottom of the mold against the base of the mold. Bycasting, the mold is then -filled with an insulating material diiferentfrom the insulating material used for the layer 20. The differencebetween these materials is that the thermal conductivity or thermalcoeflicient of heat transfer of the material now cast into the mold l5is lower than the thermal conductivity or thermal coeicient of heattransfer of the lmaterial of the layer 20. The material which is nowcast into the mold 15 ills'the mold to approximately the level of thetop surface of the upper connectors 22. Thus, the surfaces of 'the upperconnectors 22 and the surfaces of the lower the device have the featureof simplicity and the advantrage of affording ease of construction.While I have shown two forms of thermoelectric devices according to myinvention and methods of making such devices, various components andelements useful in such devices, as well as variations in the methods ofmaking the devices, all coming within the spirit of the invention will,no doubt, readily' suggest themselves to those skilled in the art.Hence, l desire that the foregoing be considered merely as illustrativeand not in any limiting sense.

W hat is claimed is:

l. A thermoelectric panel which comprises a plurality of bodies of-thermoelectric material spaced from cach other and each having oppositeend surfaces facing in opposite directions, a layer of solidifiedcasting resin enveloping and adhering to a central portion-of eaclrofsaid bodies, connectors -electricallyrjoining different pairs of saidend surfaces lto establish an electrical circuit, Vand at least oneother layenof solidified casting resin Abetween said opposite endsurfaces andsurroundingsaid bodies of thermoelectric material and saidtirst'named layer,ysaid first named layer having a higherVrthermal:conductivity than said other layer.

2. rlhe panel as set forth inclaim 1 Whereinsaid'casting resins are ofthe epoxy resin type.

3. A thermoelectric device which comprises a plurality of bodies ofthermoelectric material disposed in ordered array, a bonding layer ofmaterial comprising a solidified epoxy casting resintsurrounding andadhering to a central portion of each of said bodies to maint-ain saidbodies in said ordered arra a plurality of conductive terminals securedbetween different pairs of said bodies at the opposite ends thereof toestablish an electrical circuit through said bodies, and other layers ofmaterial comprising another solidiied epoxy casting resin having -athermal conductivity lower ythan that of said first-named resin, saidother layers being disposed between said opposite ends of said bodiesand around said first named layer.

4. A method of making a thermoelectric device including a plurality ofbodies of thermoelectric material which comprises the steps of casting alayer. of liquid casting resin around intermediate portions of saidbodies, causing said resin to solidify and adhere to said bodies,connectelectrical terminals between different ends of said bodies,casting another liquid casting resin having a thermal conductivityhigher than the thermal conductivity of said first-named resin aroundsaid bodies and said soliditied layer, and `causing said other materialto .solidify thereby providing a matrix of said thermoelectric bodies.

5. A method of making va thermoelectric device including a plurality ofelements of thermoelectric material whichtcomprises arranging saidelements in ordered array in a mold having a first cross-sectional area,casting a "ist liquid resin into said mold, permitting said resin toolidify into a layer which binds said thermoelectric elements into a'iitary structure, removing the bound ther` ino-electric elements fromsaid mold, `connecting conductive Iterminals between said ,elements atopposite ends thereof, placing the connected, bound thermoelectricelement into another mold having a second cross-sectional area largerthan said rst cross-sectional area. with the connectors at one end ofsaid elements disposed against the base of said mold, casting anotherliquid resin having a lower thermal conductivity than that of said firstresin into said last-named mold to envelop said bound thermoelectricelements while leaving the surfaces of said terminals exposed, andpermitting said other resin to solidify.

6. A method of mak'ng a therrnoelectric device includng a plurality ofelements of thermoelectric material which comprises arranging saidelements in ordered array mold having a first cross-sectional area,casting a in a rst liquid resin into said mold, permitting said liquidresin to solidify into a layer which binds said thermoelectric elementsinto a unitary structure, removing said bound thermoelectric.elementsfrom said mold, connecting conductive terminal-s between said elementsat opposite-ends thereof, placing a plate of conductive materialhaving-an electrically insulating coating on at least one face thereofinto another mold on the baseof said other mold with said one faceexposed, placing said connected, bound thermoeleotric elements into saidother mold with the connectors at one end of said element in contactWit-l1 said one face of said plate, placing another plate lof conductivematerial having an electrically insulating coating on at least one facethereof against the terminals 'at-the other ends of said elements withsaidzone face of said other plate in contact with said terminals,casting another liquid resin having a lower thermal conductivityr thansaidV first resin into said last-named mold `to envelop said boundthermoelectric elements said terminals and said plates while leaving thefreesurfaces of said plates exposed, and permitting said other castingresin to solidify.

7. -A method of making a thermoelectric device including a, pluralityoftbodiesrof thermoelectricmaterial Which comprises the, steps ofcasting a layer including an epoxy casting resin around intermediateportions of-said bodies, causing said resin tosolidify and adhere -tosaid-bodies, connecting electricalterminals'between different-ends ofsaid bodies, casting-another material containing anepoxy castingresinhaving a thermal.conductivityhigher than the thermal conductivity ofsaid first named epoxy lCasting resin around said bodies and said layer,and causing said other material to solidify thereby providing a ymatrixof said thermoelectric bodies.

8. A method of making a thermoelectric device including a plurt lity ofbodies of ther-moelectricl material which comprises arranging saidbodies in ordered array in-a mold, pour-ing a material having a lowmeltingpointinto said mold to cover a predetermined portion of saidbodies, casting airst epoxy resin into said mold over said low meltingpoint material, causing said epoxy resin to solidify so as tobindsaidthermoelectric bodies into a unitary stnicture, removing saidbound'together thermoelectric bodies from said mold, heating said boundthermoelectric elements to melt and remove said low temperature-materialtherefrom, connecting conductiveterminals between said bodies atopposite ends thereof, again placing 4said connected boundthermoelectric elements in a mold with the connectors at one end of saidbodies disposed. against the base of said mold, castinganother'epoxyresin having a lower thermal conductivity than said first epoxy resininto said last named mold to envelop said bound thermoelectricbodieswhile leaving the surfaces of said terminals exposed, and causing saidother epoxy resin to solidify.

9. A method 4of making a thermoelectric device including a plurality ofelements of thermoelectric material which comprises arranging saidelements in ordered varray in a mold, casting a first epoxy resin intosaid mold, permitting said epoxy resin to solidify to-bind saidthermoelectric elements into a unitary structure, removing said boundtogether thermoelectric elements from said mold, connecting conductiveterminals between said elements at opposite ends thereof, again placingsaid connected bound thermoelectric elements in a mold with theterminals at one end of said elements disposed against the base of saidmold, casting another epoxy resin-having a lower thermal conductivitythan said first epoxy resin into said last'named mold to envelop saidbound` thermoelectric elements while leaving the surfaces of saidterminals exposed, and permitting said other epoxy resin to solidify.

l0. A method of making a thermoelectric device including a plurality ofbodies of thermoelectric material which comprises arranging saidbodies'in ordered array in a mold, pouring a 'lirst material into saidmold to cover about one-third of said bodies, casting a vliquid plasticmaterial into said mold over said first material to cover about anadditional one-third of said bodies, permitting saidplastic to solidifyto bind said thermoelectric bodies into a unitary structure, removingsaid-bound together aardbei connectors 22 will be exposed and notcovered by the material now cast into the mold 15.

The latter casting material may be a plastic. A plain epoxy resin orcement will be suitable. Such resins are self-setting at roomtemperature and simplify the construction of the device. A suitableepoxy resin is Araldite This epoxy resins may be clear and uncolored.The characteristic of this epoxy resin which makes it preferred for usein manufacturing the device provided by the invention is that it has alower thermal coeiiicient or thermal conductivity than that of thematerial used for the intermediate layer 20.

It has been found that the use of a dual layer structure comprising anintermediate layer of material having higher thermal coeiicient andthermal conductivity than that of the material used for the outer layers28 and 30 increases the efficiency of the thermoelectric device andincreases the temperature drop obtainable with the device as measuredfrom the hot junction to the cold junction. The hot junction, it will beappreciated, is formed by the connectors 22 on one side of thethermoelectric device and the cold junctions are formed by the connector22 on the opposite side of the thermoelectric device for current ilowthrough the bodies of thermoelectric material in one direction. The hotand cold junctions reverse for current ilow in the oppositeV direction.While the reason for such increased eiiiciency and increased temperaturedrop has not been ascertained at this time, a probable theory is thatthe layer of higher thermal conductivity permits the dissipation ofloulean heat from the bodies while the layers or" lower thermalconductivity prevent the back ow of heat from the hot junctions to thecold junctions.

After the material cast into the mold l5 on opposite sides of the layer20 has solidied and set, the entire device may be removed from the mold.The upper and lower surfaces of the device which are in the plane of theconnectors 22 may be bufted to insure that none of the epoxy resinadheres to the connectors. lt will be observed that the thermoelectricdevice which has been provided -by the practice of the processillustrated ln connection with FIGS. 1 to 4 is a matrix of thermocoupleelements. By the term matrix is meant the enveloped elements from whichthermoelectric eects may be derived. The term matrix also applies to theordered array of elements which are assembled in accordance with thepractice of the invention.

It will be observed that the matrix may be sub-divided into smaller'units by merely cutting or sawing through the layers of envelopinginsulating plastic material 23, Z0 and 30 between adjacent bodies l@ and312. rthe layers 2.8 and 30 are provided upon solidication of the final:asting resins and these layers extend from the opposite sides of theintermediate layer Ztl to the end faces of the :onnectors 22 on the coldand hot junction sides of the natrix.

The thermoelectric matrix may be readily applied as 1 heat pump. Thesurface of the matrix containing the lot junction connectors 22 may bedisposed against the Jody to be cooled. For example, the cold junctionsur- I'ace may form the walls of a refrigerator chamber. Suit. ible heatdissipating means, such as ns or a large conluctive element, may bedisposed adjacent the hot junc- `ion surface of the matrix. It should benoted, however, hat insulation should be provided between the connectorsi2 and a conductive heat dissipating member. Such insuation may be athin sheet of plastic material as described n a patent, No. 2,872,788,issued in the name of Nils E. .indenblad on February l0, 1959.

Another embodiment of the present invention ywherein teat is dissipatingmembers may be assembled integrally Vith the matrix is shown in FIG. 6.The bodies di? and 'r2 of P-type and N-type material, respectively, areshown naintained in properly assembled relationship by a pluality oflayers of insulating material 44, 46 and 4S. The

5 intermediate layer 44 desirably has a higher thermal conductivity thanthe outer layers 46 and d8 and a lower coeicient of expansion.

Plates 50 and 52 of conductive material having excellent thermalconductivity are assembled integrally with the matrix. The illustratedplates 5@ and 52 are anodized aluminum. The plates are anodized in orderto provide electrical insulation. The plates Sil and 52 are disposed incontact with the hot junction connector terminals Sli and the coldjunction connector terminals 56, respectively. During the nal castingprocess, when the layers de and 48 are formed, additional casting resinis added to cover the edges of the plates 56 and 52. The castingmaterial 4bonds with the plates and enters within the notches 69. Sidelayers 58 and 59 are therefore provided which adhere to the end ones ofthe bodies of thermoelectric material 40 and 42 and to the edegs of theplates Si? and 52. The plates 5l) and 52 provide large area heatdissipating and heat absorbing terminals. The thermoelectric panelmatrix, including the integral plates and the bonding layers, is verysturdy and may be used directly in heating, cooling or power generatingequipment. The plates Si? and 52 will provide the hot or cold surfaces.When power generation is desired, a temperature gradient may beestablished across the panel by heating either the plate 5t) or 52.

Another method of 'the manuacture of a thermoelectric device provided inaccordance with the invention may be practiced. ln accordance with thismethod, the connectors 2.2 may be initially soldered to the lower endsof `separate pairs of the l? and N ,type bodies lil and l?. so as toprovide la number `of pairs of P and N type bodies having connectorplates at one end thereof. These bodies may be arranged in the mold withthe connector plates disposed at the bottom of the mold. The arrangementmay be in an ordered array as previously described. rlhe layer of epoxyresin 3Q may then be cast into the mold. rthis layer will cover theconnectors 2?. and may extend to yapproximately `one-third the height ofthe bodies.` lt will be observed that a layer of wax -is not used inpracticing this method of making a therrnoelectric device -provided bythe invention. After the layer 3d has solidified, the intermediate layerZtl may be cast. Upon soliditlcation of the intermediate layer Ztl, theother connectors 22 may be soldered to the exposed end of the bodies ofthermoelectrio material lb and l2. When the solder is cooled )and theconnectors are permanently attached to the bodies, the final layer ofepoxy resin may be cast into the mold. When this nal layer has solidiedand set, the assembled matrix of thermoeiectric elements may be removedfrom the mold. it will be observed that the foregoing method simplifiesthe construction of the thermoelectric matrix to some extent.

ln making a thermoelectric device similar to the device described inconnection with ldlG. 6 of the drawing, the foregoing meth-od will bepracticed. However, an initial step in practicing the method will be toplace the anodized aluminum plate 52 at the bottom or the mold. Then,the pairs of bodies of thermoelectric material having the bottomconnectors Sd attached thereto may be placed in ordered array on theupper surface of the aluminum plate 52. The lower intermediate layers ofepoxy resin may then be cast, successively, into .the mold. Followingsoldering of the other connectors do to the exposed ends ol Ithe bodiesof thermoelectric material, the upper anodized aluminum plate S@ may beplaced on top oi the upper connectors 5d and the final layer of epoxyresin cast into the mold. The completed device may then be removed fromthe mold.

From the foregoing description, it will be apparent that l have providedan improved therrnoelectric device and several methods of making thesame. The device is more rugged, more easily handled, more efficient andmore readily miniaturized Ithan other thermoelectri-c devices which arenow available. The methods of making thermoeleetric bodies from saidmold, removing said rst material from said bound thermoeleetricelements, so1dering conductive terminals between said bodies at oppositeends thereof, again placing said connected bound thermoelectric bodiesin a mold with the connectors at one end of said bodies disposed againstthe base of said mold, casting another liquid plastic material having alower thermal conductivity than said rst epoxy resin into said lastnamed mold to envelop said bound thermoelectrio bodies while leaving thesurfaces of said terminals exposed, and permitting said other plasticmaterial to solidify to provide a matrix of thermoeleetric bodies.

References Cited in the le of this patent UNITED STATES PATENTS PetrikMar. 8, 1932 Telkes July 7, 1942 Hunrath Jan. 27, 1953 Eich Feb. 8, 1955Fisher July 26, 1955 Lindenblad June 12, 1956 Lindenblad Feb. 10, 1959Goldsmid May 12, 1959 Lindenblad Sept. 15, 1959 Fritts Sept. 29, 1959

1. A THERMOELECTRIC PANEL WHICH COMPRISES A PLURALITY OF BODIES OFTHERMOELECTRIC MATERIAL SPACED FROM EACH OTHR AND EACH HAVING OPPOSITEEND SURFACES FACING IN OPPOSITE DIRECTIONS, A LAYER OF SOLIDIFIEDCASTING RESIN ENVELOPING AND ADHERING TO A CENTRAL PORTION OF EACH OFSAID BODIES, CONNECTORS ELECTRICALLY JOINING DIFFERENT PAIRS OF SAID ENDSURFACES TO ESTABLISH AN ELECTRICAL CIRCUIT, AND AT LEAST ONE OTHERLAYER OF SOLIDIFIED CASTING RESIN BETWEEN SAID OPPOSITE END SURFACES ANDSURROUNDING SAID BODIES OF THERMOELECTRIC MATERIAL AND SAID FIRST NAMEDLAYER, SAID FIRST NAMED LAYER HAVING A HIGHER THERMAL CONDUCTIVITY THANSAID OTHER LAYER.